We changed our to a full Queen (60" X 80") before we ever left the driveway. Think about the thickness (head room getting up can be an issue). I also added a piece of 3/8" plywood that simply covered the original shorter piece from the storage compartment hinge back. That helps to support the extra 6" of length.
I just wanted to update. After a year of the regular sized queen we notice some sag in the last 5 inches. I simply removed part of the plywood based and reinstalled a longer piece. Sleeps great.